Spark plug



Oct. 10, 1944. GWM. PAuLsoN SPARK PLUG Filed July 15, 1929 2 Sheets-Sheet 1 l 65 "56 27 i 57 i9 i791 25 24 l 5.1 I \l\ l l 5A l /l ,'/1 /f/,ff 16 #nv /l l /I l f l f 5 40 v 25 22 53 26 26| 50'5 4\ 3 xm Z 5;; 19W .'/l/l//l /WQ'N 6i W5* 7a 4 l* V" 1 7 1 o L 12 l Oct'. 10, 1944. G. M. PAuLsoN SPARK PLUG 2 Sheets-Sheet 2 Filed July l5, 1929 i W [NI/ENTOR ATTOR EY Patented Oct. l0, 1944 PATENT OFFICE,

assasvz' SPARK PLUG George M. Paulson, New York, N. Y., assigner to The B. G. Corporation, New York, N. Y., a corporation of New York Application July 15, 1929, semi No. arazzi 24 anims. (ci. 12a- 169) The present invention relates to spark plugs, and particularly to shielded plugs for use in high compression airplane engines located in relatively close proximity to the highly sensitive radio-receiving sets carried by airplanes.

It is well known that the high tension ignition current in an engine ignition system sets up electrical disturbances which cause serious interference with the reception of signals in an adjacent radio-receiving set, in some instances rendering receptionsubstantially impossible, and it is f urther known that such interference may be eliminated if the high tension current carrying elements of the system are entirely surrounded by a metallic shield, grounded to the motor, which serves to absorb the high frequency discharges affecting radio reception.

Furthermore, the service conditions imposed on spark plugs for airplane motors are exceptionally severe, as the high compression ratios employed and the prevalent use of air cooling result in extreme combustion chamber and cylinder temperatures, the effects of which the plugs must be able to withstand. Also, the usual exposed position of the plugs require that they -be fully shielded in order to prevent short-circuiting of the high tension current due to moisture from rain, snow or sleet on any of the exposed parts, or through deposits of oil thrown from the engine or of salt from sea spray. In addition, the

that the several elements comprising the plug be assembled into a substantially integral unit able te withstand not only extreme vibration but also relatively sudden and wide temperature var iations and stresses resulting from heating without loosening.

The principal objects of the invention are, therefore: to provide a compact plug having an integral assembly in which the high tension spindle is held in insulated relation Within the outer elements of the plug without resort to screw threaded or equivalent mechanical fittings; to provide a plug in which assembly is effected and maintained by pressure; to provide a construc-` tion adapted for complete metallic shielding grounded to the motor; to provide a plug adapted to withstand high combustion chamber pressures and temperatures without failure; to provide a plug of this character in which mica'is employed in a highly effective manner as a compressible material of high dielectric strength for the insulating medium; to provide a plug and cable assembly completely shielded against possibility of short circuit due to the presence of exterior moisture or foreign deposits of any kind; and to provide a shielded plug of the above character which is substantially as compact as the ordinary unshielded plug.

These and other more detailed objects of the invention will become apparent from a consideration of the illustrative forms of the invention hereinafter more fully described with reference to the accompanying drawings forming a part hereof.

In the said drawings:

Fig. 1. is a vertical section on an enlarged scale of a preferred form of plug;

Figs. 2 and 3 are sections taken, respectively, on the lines 2-2 and 3 3 of Fig. 1;

Figs. 4 and 5 are side and end elevations, respectively. of the cable terminal connection shown inFig. 1;

Fig. 6 is a vertical section, enlarged, of another form of plug;

Figs. '1 and 8 are side and end views, respectively, of the cable terminal connection shown in Fig. 6;

Fig. 9 is a vertical section of a third form of plug; and

Fig. 10 is a section taken on the' line lll-l0 of Fig. 9.

Referring now to Fig. l, the plug comprises a cylindrical central spindle I, preferably made from steel having a high heat-conducting characteristic, the upper portion of which is preferably corrugated by a seriesof circumferential grooves 2 and the lower end of which'terminates in an enlarged semi-spherical head 3 from which the center electrode 4 projects. The head 3 is preferably`of special non-scaling steel welded to the spindle, and the electrode 4 of an alloy such as manganese-nickel especially'adapted to withstand erosion due to the spark arc.

The spindle l is surrounded by a mica insulating tube 5, which it will be noted extends for a considerable distance above the upper end of the spindle. The lower end of the mica sleeve is surrounded by a number of mica washers 6, which are held in place between the shoulder formed by the enlarged spindle head 3 and an annular cylindrical brass sleeve 1. the lower end of which is enlarged to form the conical portion 1".

The usual steel shell 8, threaded exteriorly at 9 and 'provided with a suitable electrode Ill, is formed with -a conical gasket seat ll, between which and the coupling nut I2 the soft copper gasket I3 is -placed to form a gas-tight seal. The lower conical portion 1 oi' sleeve 1 fits the` correspondingly tapered bore I4 in nut I2, and the upper cylindrical portion of sleeve 1 is surrounded by the brass barrel I5. Barrel I5, it will be noted, extends above the top of spindle I, as do tube 5 and sleeve 1, the portion above the spindle having a smaller outer diameter than that surrounding the spindle. A circumferential groove I8 is located between the portions of different diameter.

The arrangement of the structure just described, with the exception of the shell l, forms an important feature of the invention, the assembly preferably being accomplished as follows:

The mica tube 5 is rolled on spindle I, preferably with sumcient pressure to cause it to press into grooves 2.- Mica. Washers 5 are then slipped over the tube, followed by sleeve 1, the latter being then forced into the conical bore I4 of nut I2 with suillcientforce to form a tight joint. The barrel I5 is then placed over the upper end of sleeve 1 and an annular die drawn over. the lower and larger diameter portion of the barrel to compress it, and with it sleeve 1 and tube 5. A tremendous lateral pressure is thus exerted, forcing the insulation into the spindle grooves and causing the metal in sleeve 1 and barrel I5 to take a permanent set which binds the several elements tightly and permanently together. It will be apparent to those skilled in the art that with a properly proportioned die, suillcient lateral pressure may be exerted to bind the elements together without the aid of the spindle grooves to prevent longitudinal movement.

In ordinary, or unshielded, spark plugs, in which the spindle extends above the top of the plug to receive a nut, it issimple to lock the parts in assembly. In the kind of spark plug to which the present invention relates a more dilcult problem is presented. It is essential that the parts of the plug remain in tight and solid assembly notwithstanding the high temperatures and pressures and the great vibration to which the spark plugs are subjected in aviation 45 engines particularly. The forces tending to cause slipping or loosening are especially severe when the spindle is insulated in the highly effective manner shown in the drawings, that is to say by mica wrapped about the spindle and by a stack of mica discs held under compression between the head of the spindle and a shoulder afforded -by some part of what may be termed the body of the spark plug. This mica has a relatively large coeilicient of expansion and when highly heated exerts a very great force tending to pull the spindle downward in the plug. This loosening force is to be resisted without the aid of a top nut or the like, and that is accomplished by 'providing for a tremendous inward compression of a sleeve or barrel which extends above the upper end of the spindle, or of two metal elements surrounding the upper part of the spindle and its wrapped insulation. This permanent compression or distortion of the metal enclosure must extend over an appreciable length in order to be adequate as the sole locking of this assem- 'I'he assembly thus formed results in a substantially integral unit, much superior to corresponding units in prior known forms of plug, which in some instances have employedcompressed metal rings to dbtain a gas-tight seal,

but which. have relied on threaded or equivalent lthe unit in insulating material I8 is fitted over the upper end of barrel I5 and held in place by the crimped end I9 fitting into the groove I8, this couplingl while holding the elbow against longitudinal displacement, permitting the elbow to be rotated about the axis of the'barrel.

As will be clear from Fig. l, the Bakelite in one arm of elbow I1 is counterbored to permit the reception of the upper end of barrel I5, there being left a central cylinder of Bakelite 25` which extends into the end of tube 5 above spindle I.

blage, without breaking or cutting the relatively brittle mica. The portion compressed by a diedrawingoperation should be cylindrical, or virtually cylindrical, and-should be of substantial length for eii'ective results.

Other specific means for permanently deforming or setting the metal, such, for example,` as a rolling operation, may be employed.

A recess 2l is provided in the upper end of spindle I into which the brass wire or pin 22, carried in a bore through cylinder 2li, extends. Obviously the pin 22 is locked in position upon assembly of the plug and elbow.

The Bakelite in the other arm of elbow I1 is recessed as at 23, and a short bore 24, oil'set with respect to the axis of 23, serves to expose the upper end of pin 22. A small coil spring 25, preferably of bronze, and with its inner end contacting with pin 22, extends through bore 24 into recess 23.

From the foregoing it will be seen that elbow I1, barrel I5, sleeve 1, coupling nut I2, and shell 8 form a complete outer metallic casing surrounding the elements forming the path of the high tension current passing through the plug.

The wall of the free end of elbow I1 is prei'- erably thickened as shown, and a relatively shallow circumferential groove 26 of arcuate section provided therein.

'Ihe terminal fitting for the ignition cable comprises a hub 21, preferably brass, having a differential bore, in the larger end of which is secured the insulating tube 28, which may be of fabric moulded in Bakelite. Both the smaller diameter of the hub bore and the internal diameter of tube 28 are such as to form a tight ilt over the insulation forming a part of cable 2l, and the outer end of tube 28 is counterbored at 30 to receive the brass washer 3l, to which the end of the ignition cable wire 32 is soldered or otherwise secured in electrical contact. d

A thin spring brass cylinder 33 is spunat one end into a suitable recess in hub 21 and the extending end of the cylinder is slotted to form a number of ngers 34 as shown more clearly in Fig. 4. The outer ends of the ngers are belled, as at 35, and adjacent to the belled ends the fingers are crimped inwardly as at 85.

A lockring 31 is fitted over the ngers, the.

21 by means of a lock wire 40 or by soldering or brazing.

In Fig. 6 a modified form of plug isshown in which the terminal connection is axial with the plug. In this form the corrugated spindle I is surrounded by the mica. tube 5, which extends above the end of the spindle and is in turn surrounded by the sleeve 4I, the lower conical end of which is seated in the coupling nut I2. The upper end of sleeve 4I has a lower larger diameter 42 and a smaller upper diameter 43, and at its upper end is thickened to present a shoulder 44. It is to be noted that the diameter of the upper thickened end is less than at 42.

In general, the assembly of this plug is similar to that of the form shown in Fig. 1, sleeve 4I 'being set into nut I2 with sufficient pressure to assure a gas-tight seal. Spindle I and sleeve 5 are locked in place by compressing the lower larger diametered portion 42 of sleeve 4I, preferably through a die-drawing operation, which will cause a ilow of metal downward as well as inward to additionally insure a seal between sleeve 4I and nut I2. In this case sleeve 4I performs the function of barrel I5 shown in Fig. 1.

A brass cable terminal hub 45, slotted to form fingers 46, is tted tightly around the ignition cable, the braided wire center 32 of which passes through a brass washer 41, secured in place by a screw 48. A mica or other insulating tube 49 is held between washer 4l and a recess 50 in hub 45.

The shielding for the ignition cable is secured by a lock wire 5I in a groove in hub 45, while ilngers 46 are curved inwardly at their ends to snap over shoulder 44. A safety lock wire seated in groove 52 may be used. v

In Fig. 9, another variation is shown. In this form, the mica tube 5 around spindle I is not extended above the upper end of the latter, and the spindle and tube are set into the coupling nut I2 with a conical brass ring 53, Whichvis sulciently compressed to form a gas-tight seal. The coupling nut I2 is provided with an undercut recess 56 into which the lower end of brass sleeve 54 extends, this sleeve being lined with a mica tube 55. Spindle I, mica. tubes 5 and 55 and metal sleeve 54 are locked in assembly by compressing sleeve 54, preferably by a die-drawing operation, which will cause the metal of the latter to ow into the recess 56. Alternately, sleeve 54 may be attached to nut I2 by rolling its lower end into the recess 56.

If the lower end of sleeve 54 is, as shown, smaller in diameter than the shouldered portion 44, a split die may be used for the drawing operation.

In this form, the same type of terminal connection as that described in connection with Fig. 6, may be employed.

From the foregoing description it will be seen that the present invention provides a form of plug which meets the severe conditions imposed on plugs in the class of service for which it is intended, and that the outer and inner metallic parts of the plug and the conductor are thoroughly and effectively insulated. From an inspection of tthe several figures, it will be apparent that in no case is there an uninsulated air gap between the high and low potential elements of less than the minimum length of five-eighths of an inch required to prevent short-circuiting of the ignition current; except, of course, at the plug electrodes.

Furthermore, the construction according to the invention provides a mica-insulated shielded high-tension unit which is, after assembly, 'substantially integral and therefore not subject to the possibility of loosening or disassembly due to backing of! oi nuts because of motor vibration, as is the case with heretofore known forms of mica plugs.

In addition, the improved form of plug is very compact.

I do not claim in this application a construction in whichthe insulated high tension conductor is inserted into a mica-lined socket of the metal body of the spark-plug, and in which, further, a mica tube is placed on this portion of the conductor so as to act as a spacer between a detachable connection or terminal at the top and a tip-piece fastened to the lower end of the conductor, that being claimed in my application Serial No. 479,684, led September 4, 1930.

While I have in accordance with the Patent Statutes described the best examples of the invention known to me, it will be obvious that many changes and modifications may 'be made in the illustrative embodiments shown without departing from the spirit of the invention, which is to be considered as limited only by the scope of the appended claims, and it will further be apparent that certain features of the invention may be employed without the use of others.

I claim:

1. In a spark plug, a cylindrical metal spindle, a mica tube around substantially the entire length of said spindle, a sleeve of relatively ductile metal around substantially the entire length of said tube and having an exteriorly tapered lower portion, said sleeve being permanently compressed above said tapered portion to grip said mica. tube and metal spindle against longitudinal displacement, and a member of relatively hard metal in which the lower tapered portion of said sleeve is compressed to eiect a seal.

2. A spark plug comprising an interiorly and exteriorly threaded metal shell, a cylindrical metal spindle providing a terminal for receiving an ignition current, a mica tube around said spindle and extending beyond the terminal end of the spindle to provide a socket for an ignition cable,

a sleeve of relatively ductile metal around sub-- stantially the entire length of said tube, said sleeve being permanently compressed to permanently grip said mica tube and metal spindle against longitudinal displacement, and an annular coupling nut engaging the lower portion of said sleeve and screwed into said shell.

3. In a spark plug, a cylindrical metal spindle having an upper terminal end adapted to receive an ignition current and a lower shouldered end carrying an electrode, a mica tube around said spindle, a plurality of mica washers surrounding the lower portion of said tube, a metal sleeve having an outwardly tapering lower portion, said sleeve surrounding said tube above said washers, a coupling nut around the tapered portion of said sleeve and having a tapered bore receiving the same, and an outer metal barrel around the upper cylindrical portion of said sleeve,` saidl barrelbeing permanently compressed to grip said sleeve and. said tube around the upper portion of said spindle, whereby a substantially integral assembly is produced, a shell into which said coupling nut is screwed, and a second electrode on said shell.

a tube of insulating material surrounding said spindle and an annular member surrounding said tube, at least a portion of said member being permanently compressed around said corrugations to permanently grip said spindle and tube against longitudinal displacement with respect to each other and to said members.

5.,A spark plug, comprising, in combination, a central spindle having a head at its lower end, a metal bow including a part which extends upward around the upper part ofthe spindle and above its upper end, an insulation of wrapped mica about the spindle extending from said head to a point above the spindle, and a further insulation of mica discs conilned between said head and a shoulder in `the body, said metal part having been permanently compressed over a substantial length so as to grip the wrapped mica insulation and the spindle powerfully in rigid',

non-loosening assembly with the metal part.

6. A spark plug, comprising, in combination, a central spindle having a head at its lower end, a shell, a coupling nut threaded into said shell. a sleeve united with said coupling nut and extending upward around the u pper part of the spindle and above its upper end, an insulation of wrapped mica about the spindle and likewise extending above its upper end, and a further insulation of mica discs held under compression in the shell above the head of the spindle, said sleeve having been permanently compressed over a substantial length so as to grip the wrapped mica insulation and the spindle in rigid, nonloosening assembly with the sleeve.

7. A spark plug, comprising, in combination, a central spindle having a head at its lower end, ashell, a metal sleeve extending upward around the upper part of the spindle and above its upper end, the lower end of said `sleeve having an enlargement, a coupling nut screwed into the shell and engaging the enlarged lower end of the sleeve to hold it to the shell, an insulation of wrapped mica about the spindle and likewise'extending above its upper end, and a further insulation of mica discs held under compression in the shell. above the head of the spindle, said sleevehaving been permanently compressed over a substantial length so as to grip the wrapped mica insulation and the spindle in rigid, non-loosening assembly mica discs conilned under compression by and between the head of the spindle and the lower end of said metal sleeve, said sleeve having been permanently. compressed over asubstantial length so as to grip the wrapped mica insulation and the spindle in rigid, non-loosening assembly with the sleeve.

9. A spark plug, comprising, in combination, a central spindle having a head at its lower end, a body including a sleeve extending around the upper part of the spindle and above its upper end, an insulation of wrapped mica about the spindle extending from said head substantially to the upper end oi' the spindle, a second insulation of wrapped mica lining said sleeve, and extending from below the upper end of the tlrst insulation to a point above the upper end of the spindle. and an insulation of mica discs held under compression above the head oi the spindle.

10. A spark plug, comprising, in combination, a central spindle having a head at its lower end, a body including a sleeve extending around the upper part of the spindle and above its upper end, an insulation of wrapped mica about the spindle extending from said head substantially to the upper end of the spindle, a second insulation of wrapped mica lining said sleeve, and extending from below the upper end ot the ilrst insulation to a point above the upper end of the spindle, and an insulation of mica discs held under compression above the head of the spindle, said sleeve having been permanently compressed to grip the two wrapped mica insulations and the spindle in rigid, non-loosening assembly with the metal sleeve.

11. A spark plug comprising a. spindle having an annular circumferential groove therein, a tube of insulating material surrounding said spindle and an annular member surrounding said tube,

at least a portion of said member being perma...

12. Ina spark plug having a body having a barrel forming a socket for the insertion of an insulated tension conductor, an insulating sleeve Within said barrel, and a metal member engaging and protecting the upper end of said sleeve.

13. In a spark plug having a shell and a central spindle insulated from the shell, the combination of a metal barrel with insulation lining extending upward from the shell above the upper end of the spindle to providea socket for the insertion of an insulated lead into electric connection with said spindle, a connection through which the lead is passed and which has detachable connection with said barrel and an insulating tube about the portion of the insulated lead within said socket, said tube being connected to the lead and arranged to engage at its upper end with said connection.

14. A cap for spark plugs having a sleeve adapted to receive an ignition cable, means to secure the ignition cable to the sleeve to project below the sleeve and into the spark plug, means for securing the sleeve to a cylindrical element of a spark plug, and a protective sleeve carried by the cap and spaced between the spark plug and lthe portion of the ignition cable below the sleeve.

' 15. A cap for spark plugs having a sleeve adapted to receive an ignition cable, the sleeve being formed with a. bore forming a restricted portion and a shoulder, mean to secure the ignition cable to the sleeve, means for securing the sleeve to a cylindrical element of a spark plug, and a protective sleeve carried by the cap and seated against the shoulder.

16. A cap for spark plugs having a sleeve adapted to receive an ignition cable, the sleeve being formed with a. bore forming a restricted portion and a shoulder, means to secure the ignition cable to the sleeve, means for securing the sleeve to a cylindrical element of a spark plug, a protective sleeve carried by the cap and seated against the shoulder, and means to secure the protective sleeve against the shoulder.

1'7. A cap for spark plugs having a sleeve adapted to receive an ignition cable, means to secure the ignition cable to the sleeve, means for securing the sleeve to a cylindrical element of a spark plug, and a protective sleeve carried by the cap, the bore of the protective sleeve being at least as great as that of the first sleeve.

18. In a spark plug, the combination of a tubular metallic jacket of high heat conducting capacity, a spindle in the jacket, projecting therefrom and provided at its lower end with an electrode, insulating means between the electrode andthe adjacent end of the jacket, between the spindle and jacket and extending to the top of the spindle and still other insulation constituting a tube distinct from said insulating means, insertable in the upper end of the jacket and when so inserted positioned between the spindle and jacket and extending to the top of the jacket and means for securing said tube to the jacket.

19. In a spark plug, the combination of an air cooled open top metal jacket, a spindle extending axially of the jacket and provided at its upper end with means within the outlines of the jacket for connection with an electric lead, insulating means surrounding and engaging the spindle, other insulating means lining the upper portion of the jacket bore, extending above the upper end of the spindle and adapted to enclose the intruded end of the electric lead, and an electric lead provided at its intruded end with a sleeve secured thereto and forming a third insulation positioned for the most part in the jacket above the spindle and adapted to position insulation between the intruded end of the electric lead and the insulating means which lines the jacket and a metallic member for securing said sleeve to the jacket.

20. In a spark plug, the combination of a shell provided with an electrode, a unit including a spindle constituting an insulated coacting electrode and a barrel extending above the spindle to form a socket, an insulated electric lead having a flexible metal covering, a metal tubular member through which said conductor is passed and to the outer end of which said metal covering is electrically connected, the end of the insulated lead being inserted in said socket to make electrical connection with the spindle, and a terminal on the inner end of said tubular member, locking detachably with said barrel andl forming a swivel connection between the tubular member and the barrel.

21. A spark plug including a supporting tubular shell provided with an electrode, a long upstanding tubular metallic jacket having its lower end demountably positioned in the shell and in electric engagement therewith, a coacting electrode centered axially in the jacket and insulated therefrom, said jacket having its upper end open to provide a socket for the insertion therein of a high tension lead, an insulating sleeve outlining said socket, a connecting sleeve extending above the jacket secured to the high tension lead and readily separable swivel means for securing said connecting sleeve to the upper end of the jacket.

22. In a device of the class described, the combination of two readily separable parts, one of said parts comprising a spark plug and including an open top jacket and a spindle in the jacket, and the other part comprising an electric lead having an end portion intruded into the open top of the jacket and electrically connected to the spindle, a metallic sleeve secured to the electric lead externally of its intruded end portion and movable therewith and an insulating sleeve telescopically engaging the intruded end portion of the lead and swivel means for securing the Ine-- tallic sleeve to the jacket to connect the parts together without materially rotating the electric lead relative to the spark plug.

23. Means for fastening an electric lead on a spark plug comprising a metallic sleeve having its upper end shouldered, an electric lead having a metallic covering, an end of said lead extending beyond its covering and intruded into said sleeve, a telescopic tubular swivel connection through which the lead extends with one tubular part secured to the lead and the other tubular part in engagement with the shouldered end of the sleeve, and said connection including clamping means for securing in place the adjacent end o1' the metallic covering.

24. Means for fastening an electric lead on a spark plug comprising a metallic sleeve having its upper end externally shouldered, an electric lead having a metallic covering, an end of said lead extending beyond its covering and intruded into the bore of said sleeve, a swivel connection including telescopic tubular parts with one part encircling and secured to the lead and the other tubular part being internally shouldered and adapted to be disposed in engagement with the shoulder on the sleeve, and said connection including clamping means for securing i12 place the adjacent end oi' the metallic cover- GEORGE M. PAULSON. 

